There are several types of combustion nozzles provided in a combustor of a gas turbine; for instance, there are a main nozzle that is used for premix combustion and a pilot nozzle that is used for diffusion combustion; further, a certain combustor is provided with a top-hat nozzle that is used for NOx reduction during high load operation as well as combustion stability during low load operation. An example of the configuration as to such a combustor is disclosed, for instance, in the patent reference 1 (JP2008-25910); the disclosed configuration as to the combustor in the patent reference 1 is hereby explained in consultation with FIGS. 6 and 7.
Within the outer casing 102 of the combustor 100, the inner tube 104 of the combustor is anchored to the outer casing so that the inner tube is supported by the outer casing and a predetermined space is kept between the outer casing and the inner tube; the tail pipe 106 of the combustor is connected to the tip end side of the inner tube 104 so that a casing of the combustor is formed. In the middle center area of the inner casing 104, the pilot nozzle 108 is arranged; on the other hand, along the hoop direction of the inner surface of the inner tube 104, a plurality of main nozzles 110 is arranged so as to surround the pilot nozzle 108. The pilot cone 112 is fitted to the tip part of the pilot nozzle 108. Further, a plurality of top-hat nozzles 114 is arranged along the hoop direction of the inner surface of the outer casing 102.
As shown in FIG. 7, an end part of the outer casing lid part 118 is fastened to the base end part of the outer casing body 116, with a plurality of fastening bolts 120; at another end part of the outer casing lid part 118, the base end part of the inner tube 104 is fitted so that the air passage 122 is formed between the outer casing lid part 118 and the inner tube 104. Further, the tip end part of each main nozzle communicates with the main burner 124.
The top-hat forming part 126 is fitted into the outer casing lid part 118, being fastened to the outer casing lid part 118 with a plurality of the fastening bolts 128. As shown in FIG. 7, the top-hat nozzles 114 are configured in the top-hat forming part 126; namely, a plurality of fuel cavities 130 is formed along the hoop direction of the top-hat forming part 126; a plurality of first fuel passages 132 is formed from each cavity toward the outer casing lid part 118. At the front end of each first fuel passage 132, a second fuel passage 134 is formed toward the air passage 122; each second fuel passage 134 is connected to a peg 136 that is fitted to the inner surface of the top-hat forming part 126.
A pilot fuel line (not shown) is connected to the fuel port 138 for the pilot nozzle 108 and supplies pilot fuel fp into the combustor; a main fuel line (not shown) is connected to the fuel port 140 for the main nozzles 110 and supplies main fuel fm into the combustor; a top-hat fuel line (not shown) is connected to the fuel port 142 for the top-hat nozzles 114 and supplies main fuel ft into the combustor.
In the configuration described above, when the compressed air of a high temperature and a high pressure is supplied from the airflow channel 144 toward the air passage 122 along the direction of the arrow a, the compressed air is premixed with the fuel ft that is injected through the top-hat nozzles 114; the premixed air-fuel mixture streams into the inner side of the inner tube 104.
Inside of the inner tube 104, the air-fuel mixture (being premixed as described above) is further premixed with the fuel fm that is injected through the main nozzle 110, turning into revolution flow and streaming into the inner side of the tail pipe 106 of the combustor.
Further, the premixed air-fuel mixture is mixed with the fuel fp that is injected through the pilot nozzle 108 so that the finally premixed air-fuel mixture is ignited by a pilot flame (not shown), is burnt, turns into combustion gas and blows out into the inner side of the tail pipe 106; thereby, a part of the combustion gas blows out into the inner side of the tail pipe 106, accompanying the flame propagation so that the combustion gas diffuses; the combustion gas that diffuses in this way ignites the air-gas mixture that streams from the main nozzles toward the tail pipe 106; thus, the combustion continues. In other words, since the lean air-fuel mixture produced by the fuel from the main nozzles 110 can stably burns thanks to the diffusion frame propagation produced by the pilot fuel that is injected through the pilot nozzle 108, the flame propagation can be prevented from reducing inflammation. Further, the compressed air is firstly mixed with the fuel injected through the top-hat nozzles 114; this approach can bring the reduction of NOx produced in the gas turbine.
In the conventional gas turbine plants, the fuel flow rate and the airflow rate are predetermined on the basis of the generator output (demand power), the ambient temperature and so on; the fine adjustments of the operation conditions as to the gas turbine and the plant thereof are performed in the test operations or the commissioning operation; after commissioning, the gas turbine and the plant thereof are operated on the basis of the fine adjusted operation conditions. According to the conventional control device for the gas turbine plant, however, the operation state conditions cannot respond to, for example, the change of fuel contents during the operation. Accordingly, by the limitation of the ability of the conventional control device, the combustion stability is often hindered or the combustion vibrations are often caused.
In a case where combustion vibrations occur, the vibrations seriously hinder the operation of the gas turbine; hence, it is strongly required to restrain the combustion vibrations of the gas turbine as far as possible, in view of the protection of the plant facility and the enhancement of the plant availability.
The patent reference 2 (JP1993-187271) discloses a control device by which the airflow rate or the fuel flow rate as to the gas turbine combustor is controlled on the basis of the changes regarding the ambient temperature, the ambient humidity, the fuel calorific value and so on. According to the technology of the patent reference 2, in response to the technological requirement as described above, the bias control regarding the airflow rate or the fuel flow rate is made use of in order to improve the robustness for the combustion stability.
In the control means disclosed in the patent reference 2, the airflow rate or the fuel flow rate is uniformly controlled when the bias control is applied; thus, the degree of freedom as to the control is limited; therefore, it is difficult to adjust the airflow rate or the fuel flow rate so that either of the flow rates converges to an optimally controlled value.